1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for controlling a viewing angle thereof.
2. Discussion of the Related Art
Recently, LCD devices are widely used for word processors and personal computer displays in that the LCD device can be driven by a low voltage. The LCD device includes substrates treated with an alignment process, to thereby obtain a uniform picture image. In this respect, the LCD device has a directional variance, that is, the viewed image varies in accordance with the viewing direction.
For example, in the case of TN and STN mode LCD devices, the direction of light is controlled by using an alignment direction of long and thin liquid crystal molecules that has a problem of a narrow viewing angle.
To overcome this problem of directional variance in the LCD device, various proposals have been disclosed. For example, Japanese Laid Open Patent No. H9-19740 discloses an LCD device having a viewing angle control structure in which collimated light is incident on two liquid crystal display bonded to each other.
Hereinafter, a method for controlling a viewing angle in an LCD device according to the related art will be explained as follows.
FIGS. 1B and 1D are cross sectional views schematically illustrating an LCD device having two liquid crystal displays bonded to each other, on which collimated light is incident.
First, collimated light is incident on a first LCD panel 1. The first LCD panel 1 is identical in structure to a related art LCD panel that displays images.
Then, light from the first LCD panel 1 is incident on a second LCD panel 2, wherein the second LCD panel controls transmission and dispersion of the light. The transmission of light provides a narrow viewing angle mode, and the dispersion of light provides a wide viewing angle mode.
In this example, the first LCD panel is formed of a TN LCD panel, and the second LCD panel 2 is formed of polymer dispersion LCD panel.
Meanwhile, when using the high molecular dispersion LCD panel of the second LCD panel 2, as shown in FIG. 1D, liquid crystal molecules dispersed in a polymer are arranged randomly. Thus, the incident light is dispersed (6b, 6c) with the same luminance as that of surface transmitted light (6a).
In this case, a graph showing a relation between luminance and viewing angle is shown in FIG. 1C.
Meanwhile, as shown in FIG. 1B, when applying a voltage, the liquid crystal molecules dispersed in the polymer are arranged along an electric field, whereby the light is transmitted because the liquid crystal molecules are transparent.
In a narrow viewing angle mode a voltage is applied to the second LCD panel 2, and a graph for showing the relationship between luminance and viewing angle is shown in FIG. 1A. By controlling the luminance, it is possible to control the viewing angle.
In the related art, it is necessary to provide elements for collimating the light output from a fluorescent lamp and to perform additional processes for bonding the polymer dispersion LCD panel, thereby increasing a fabrication cost.
Next, Japanese Laid Open Patent No. 2004-325563 discloses an LCD device. In this case, in a vertical alignment mode, the viewing angle is controlled by changing an electrode structure. By dividing the electrode, an interval between openings is formed in-between the electrode where the liquid crystal is inclined. Also, luminance is controlled by changing the shape of electric line, to thereby change the viewing angle.
However, because the electrode structure is determined in the fabrication process, it is impossible to change the electrode structure after forming the LCD panel. Thus, several electrode shapes are compounded to thereby form pixels. Then, the pixel having the pattern with optimal viewing angle characteristics is selected, and the other pixels are not displayed, whereby the light efficiency deteriorates.
Related with the efficiency of controlling the viewing angle, as disclosed above, any effects are not made except that the maximum luminance is diverted in one direction.